This invention relates to the field of drying fabric in a rotating chamber by means of microwave energy and/or convection-heated air.
A common method of drying fabric is a clothes dryer wherein moisture-laden fabric is loaded into a chamber that is rotated while convection-heated air is drawn through the chamber. The heated air causes evaporation of the moisture which is then drawn off with the exhaust air and deposited into the atmosphere. Improvements on the convention-heated clothes dryer employ a microwave energy source which is directed at the moisture-laden fabric to heat and vaporize the moisture which is then drawn off with the exhaust air. These microwave systems are superior because they are quicker and more energy efficient. This is so because the microwave energy focuses upon the moisture held by the fabric, rather than the fabric itself, thereby accelerating the drying process and reducing shrinkage. The following U.S. patents disclose microwave fabric drying systems, some of which also have auxiliary convection heating systems U.S. Pat. Nos. 3,854,219, 4,057,907, 4,250,628, 4,490,923, 4,510,697, 4,523,387, 4,703,565, 4,829,679, and 4,896,010. Some of those dryers use a convection heating system in combination with the microwave energy source so that the microwave energy can be turned off as the clothes approach the dry condition. The convection heater then warms the air circulating through the fabric chamber to remove the last bit of moisture from the fabric. It is necessary to either incrementally throttle down or shut off the microwave energy source as the clothes approach the terminal end of the drying cycle. This is done to prevent arcing of any metal and/or electrical conductor associated with the fabric, such as zippers or golf pencils, because ,the arcing may burn holes in the fabric. Various sensors are used to detect the almost-dry condition of the fabric and communicate with a controller which shuts off the microwave source. Various patents disclose the use of sensors to monitor the humidity of the intake and/or exhaust air for the purpose of controlling the microwave energy when the clothes are nearly dry; vis: U.S. Pat. Nos. 4,334,136, 4,510,361, 4,771,156 and 4,795,871. In all of the above-described patents the sensor's output is used to control only the on/off condition of the microwave
One patent discloses using the output of a humidity sensor to modulate the pulse width of a magnetron controller thereby decreasing the microwave power as the exhaust decreases. U.S. Pat. No. 4,356,640 (col. 4, line 64 to col. 5, line 10).
To prevent leakage of microwave radiation it is necessary to seal the microwave container. The majority of microwave fabric drying systems employ "choke" seals between stationary bodies such as the access door and the main enclosure. Exemplarily, choke designs are shown in U.S. Pat. Nos. 4,313,044, 4,742,201, and 4,861,955. One patent discloses a rotary choke seal that is employed between a rotating body and a stationary body, U.S. Pat. No. 4,765,066.
Other means to improve the energy efficiency of standard fabric drying systems include recirculation systems and heat exchangers. A recirculation system, whereby a portion of the exhaust air is recirculated into the fabric chamber, is disclosed in U.S. Pat. No. 3,959,892. A heat exchanger whereby heat is exchanged between the warm exhaust air and the cooler intake air, is disclosed in U.S. Pat. No. 4,095,349.
None of the above dryers employ a full function control system that establishes a schedule of dryer operations based upon the sensor readings of the air flowing through the dryer. Additionally, none of the above dryers integrate alternative energy saving means (such as heat exchangers or recirculation systems) into the drying system under the control of the control system.
By failing to sense the condition of the intake air and use that information to customize the schedule of dryer operation the prior art systems fail to select the optimum efficiency for drying clothes and fabric.